Automatic Golf Ball Loader (better name TBD) – Part 1

Introduction to the automated golf ball loader project work. Learn about lock-in amplification and basic design techniques!

The automatic golf ball loader is (when completed) a system which can be used out on a golf range for automatically loading golf balls onto your tee after the ball is hit. The control system uses an infrared emitter and detector to determine whether or not a ball is already on the tee. If the system detects that the ball is missing, an arm will be lowered next to the tee and a ball will roll down from a feeder tray landing on the tee.

There were a few motivating factors behind this project:

  1. An opportunity to apply a technique called lock-in amplification (more on this later)
  2. A fun means of golf practice in my back yard

Developing a product that could actually be sold wasn’t really one of the motivating factors although I have thought of ways to do it along the way. I don’t believe I’ve found any home-use products that can actually do this but I’m not sure there is a huge market for it either. Commercial products exist and already exceed the functionality that I plan to complete including a user interface for lowering and raising the golf ball tee.

This project was intended to be educational and I believe projects like this are a good use of free time as long as you’re learning something.

I stumbled upon the technique of lock-in amplification in a electronics textbook “The Art of Electronics”, this is probably one of the best electronic reference books that you can buy. If you don’t have it already and are into electronics I highly recommend it! Lock-in amplification is a technique that’s used to detect a signal buried deep in noise, its actually used in detecting planets orbiting around distance stars. The following diagram illustrates how the technique works.



Unfortunately I don’t remember where I got this image from, its not mine and if someone happens to stumble upon where this came from I’d be happy to give credit where its due.

The diagram includes a formula for the multiplication of a reference signal against the input signal. What the formula is saying is that, when the input signal and reference signal match in both frequency and phase then you will get a DC voltage at the output.

What I find funny about this is that your reference signal must match your input signal. When I first read about this I was searching for why I would ever want something where I needed to know what my signal was before I could detect it. It seemed….. counter productive. However when you think about it, this technique is finding the needle in the haystack. I would love to hear from readers on how you might use something like this.


On with the project… Something that I really like to do when starting a project is to create a simple block diagram which clearly identifies the main hardware components that will be required.


In this case, the lock-in amplification will be done in the microcontroller using software. This is much easier than designing an analog multiplier which isn’t a trivial task. Besides, there doesn’t seem to be a specific advantage in doing so. This is an important trade-off for myself. I love doing things in the analog domain but only when it makes sense to do so, I don’t need unnecessary pain.

I’m going to cut this article off here. There is lots more to come including working prototypes so stay tuned! I may use the next article to talk about some testing or maybe some of the design work, haven’t decided yet!

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